Viability of dietary substitution of live microalgae with dry Ulva rigida in broodstock conditioning of Pacific oyster (Crassostrea gigas)

Abstract

The current study evaluated the microalgae replacement by dry macroalgae (Ulva rigida) in the reproductive success and biochemical composition of the Pacific oyster (Crassostrea gigas) during broodstock conditioning. Five nutritional regimes were tested: 100% macroalgae (diet 1), 50% macroalgae+50% microalgae (diet 2), 25% macroalgae+75% microalgae (diet 3) and 100% microalgae (diet 4). An unfed group was used as a negative control. The microalgae blend was composed of 33% Isochrysis galbana and 67% diatoms (75% Skeletonema costatum+25% Chaetoceros calcitrans). Gonadal maturation was reflected in the physiological condition of the individuals. All treatments, except diet 1, showed an increase in condition index and were fully matured at the end of the trial, with the best physiological condition observed in oysters fed diet 3 and diet 4. Protein and total lipid content increased during the conditioning period, whereas glycogen content decreased. Oysters conditioned with diet 3 had higher protein and total lipid content and lower glycogen content than the other treatments. In addition, diet 3 showed the highest percentage of viable veliger larvae. The current study demonstrated that it is possible to replace 25% of microalgae with macroalgae in the broodstock conditioning, minimizing the operative cost in bivalve hatcheries..

Elemental composition and bioaccessibility of farmed oysters (Crassostrea gigas) fed different ratios of dietary seaweed and microalgae during broodstock conditioning

“…A low metabolic rate is sometimes an explanation for low accumulation rates (Pavlov et al, ). Indeed, the viability results associated with this study on broodstock conditioning of C. gigas (Rato et al, ) have shown that SW100 oysters exhibited a higher mortality when compared to SW0 and the remaining feeds, being unable to meet the demands for maintenance—a lower standard metabolic rate was measured in the SW100 oysters than in SW0 oysters (Ozório et al, ). Hence, a more satisfactory explanatory hypothesis would be differences in the growth rates between the various SW groups.…”

Fatty Acid Profile of Pacific Oyster, Crassostrea gigas, Fed Different Ratios of Dietary Seaweed and Microalgae during Broodstock Conditioning

“…This is in accordance with the periods of allocation of energy to reserves followed by gonad development reported for several mollusks as a conservative strategy (Barber and Blake, ; Strohmeier et al, ). In a previous study, Rato et al () showed that oysters fed 100% macroalgae did not spawn, while the best reproductive success was observed in oysters fed with 25% macroalgae +75% microalgae and 100% microalgae diet (Rato et al, ). Due to EPA and DHA association with gametogenesis, an accumulation of these should have occurred prior to spawning.…”

“…This way and according to Rato et al (2018), when oysters are conditioned with a suitable diet, sufficient to meet nutritional requirements, such as 25% SW + 75% Alg and 100% Alg, the reserves of EPA and DHA are channeled to gametogenesis, leading to a higher percentage of viable (free-living) veliger larvae. In the case of 100% SW oysters, it seems that they mimic the behavior of C. gigas starved larvae, which selectively retained DHA during starvation, because they play other structural roles (da Costa et al, 2015).…”

Microalgal Aquafeeds As Part of a Circular Bioeconomy

“…Consequently, there is a growing trend to substitute live algae with more convenient, massproduced off-the-shelf feeds including dried algae, concentrated algal pastes, formulated feeds (including microencapsulated feeds), bacteria, and yeasts [23][24][25][26][27]. Reported disadvantages of substitute hatchery feeds have included settling, aggregation, bacterial degradation, leaching of nutrients, low digestibility of the cell wall material, cell settling, and disintegration for dried algae [23,27].…”